Ectopic heartbeat detector

ABSTRACT

A critical ectopic beat detector for providing a warning that an ectopic beat is approaching a critical portion of a heartbeat including first circuit means for monitoring a heartbeat including means for providing a first signal representative of a normal portion of said heartbeat and a second signal representative of an ectopic beat, second circuit means for measuring the time relationship between said fist and second signals, and third circuit means for providing a third signal in the event said time reaches a predetermined value to thus provide a warning that said ectopic beat is approaching said critical portion of said heartbeat, including instrumentation for presetting said predetermined value into the circuit so that the equipment may be utilized with equal facility for different patients having different heartbeat patterns, and also including an arrangement for monitoring the heartbeat on a scope and placing on the scope an indication that the ectopic beat has approached within a predetermined time of said predetermined critical portion of the heartbeat so as to enable an accurate visual observation of the change in pattern of the heartbeat.

Unite States atent rovella et al.

[4 June 27, 1972 54] ECTOPIC HEARTBEAT DETECTOR Prima Examiner-WilliamE. Kamm U S W b & G l t! t [72] Inventors: Edward A. Crovella, Snyder,N.Y.; C. A omey Ommer e er as e Verne Bariield, Mableton, Ga. 57ABSTRACT [73] Assign: Cardiac Electronics Clarence A critical ectopicbeat detector for providing a warning that [22] Filed: 23 1969 anectopic beat is approaching a critical portion of a heartbeat includingfirst circuit means for monitoring a heartbeat includ- [21] Appl. No.:887,661 ing means for providing a first signal representative of anormal portion of said heartbeat and a second signal representative ofan ectopic beat, second circuit means for measuring the timerelationship between said fist and second signals, and [51] I thirdcircuit means for providing a third signal in the event [58] Field ofSearch ..l28/2.06 A,2.06 B,2.06 F, said time reaches a predeterminedvalue to thus provide a 128/206 206 R warning that said ectopic beat isapproaching said critical portion of said heartbeat, includinginstrumentation for presetting [56] R fe n s Cited said predeterminedvalue into the circuit so that the equipment may be utilized with equalfacility for different patients UNITED STATES PATENTS having differentheartbeat patterns, and also including an ar- 3,463,143 8/1969 Karsh..128/2.06 A sj g g fzgi gz f fi xg 5 5: p ..l28 2.06 A n e cope p a as3267933 8/1966 Mms et a] preached within a predetermined time of saidpredetermined FOREIGN PATENTS OR ICATIONS critical portion of theheartbeat so as to enable an accurate 128/2 06 F visual observation ofthe change in pattern of the heartbeat. 1,264,680 3/1968 Germany 1Claim, 3 Drawing Figures F 3 f5 HLGAHSS' t i filcll fi |SOLAT|0- Lpo gCDUPLlNG II-AMFLIFIER 53:21:: JLLA- 7? TE, 3? 4 FILTER FILTER cuzcurrFlL ER cmcurr cmcunclRculT 26 Q7 5 f D|FFER 5 g 77 NEGATWE ENTIATOR H We3.1555; Q

55 5, we 56 sales, FREERUNNING COUPLER QHPARATOR NAND LATCHING SAWTOOTHPOWER LOGIC ALAS? Z GENERATOR MP- 2%! CIR I Q5 Q7 3 H S at". 9 fi' MV-a:

38, a w COMPARATOR ONE SHOT MULTlVIBRATOR as j PATENTEUJUM? m2 SHEET 2OF 2 INVENTOR.

ATTORNEY.

Edward 6?. Cvovlia Car-all u BGTBZQZJ ECTOPIC HEARTBEAT DETECTOR Thepresent invention relates to a cardiac monitoring apparatus, and moreparticularly to a device for detecting the occurrence of an ectopicheartbeat at a critical time in relationship to the remainder of theheartbeat.

By way of background a heartbeat of a normal healthy person includes theP, Q, R, S and T wave forms which are well known. However, when a personhas experienced cardiac difficulty, such as various types of heartattacks, there often occurs an ectopic beat which is an additionalrandom occurring beat. It is believed that this ectopic beat resultsfrom the irritation of the heart following damage andit occurs generallyas a reaction from the normal beat. It has been found that whentheectopic beat occurs, it very often falls between the T-wave and thesubsequent R-wave portion of the heartbeat. It occurs intermittently,that is, it does not occur as a part of every heartbeat waveform andwhen it does occur, it will generally always fall in the same locationnoted above. As long as it does not move from a position between theT-wave and the subsequent R-wave, it usually does no damage. However, ifit should start approaching the earlier T-wave so that it falls thereon,it may initiate fibrillation, which can be fatal. It has been found,however, that if the approach of the ectopic beat toward the T-wave isdetected early enough, medication can be given to the patient todesensitize the heart so that it will not keep producing ectopic beatswhich could lead to fibrillation when these ectopic beats reached theT-wave.

It is accordingly the primary object of the present invention to providea critical ectopic beat detector which detects the time relationshipbetween the critical portion of the heartbeat and any ectopic beat andprovides a warning signal in the event that the ectopic beat approacheswithin a predetermined time interval to the Twave.

Another object of the present invention is to provide a critical ectopicbeat detector which provides a visual indication between an ectopic beatand a predetermined portion of the heartbeat waveform so as to permitvisual observation for the purpose of determining whether the ectopicbeat is in fact approaching the critical portion of the heartbeat. Otherobjects and attendant advantages of the present invention will readilybe perceived hereafter.

The critical ectopic beat detector of the present invention provides awarning that an ectopic beat is approaching a critical portion of aheartbeat and comprises first circuit means for monitoring a heartbeatincluding means for providing a first signal representative of a normalportion of said heartbeat and a second signal representative of anectopic beat, second circuit means for measuring the time relationshipbetween said first and second signals, and third circuit means forproviding a third signal in the event said time reaches a predeterminedvalue to thus provide a warning that said ectopic beat is approachingsaid critical portion of said heartbeat. In addition,.

the present invention includes instrumentation for presetting saidpredetermined value into the circuit so that the equipment may beutilized with equal facility for different patients having differentheartbeat patterns. In addition, the detector includes an arrangementfor monitoring the heartbeat on a scope and placing on the scope a timeindication that the ectopic beat has approached within a predeterminedtime of said predetermined critical portion of the heartbeat so as toenable a visual observation of the change in pattern of the heartbeatwith a great degree ofaccuracy.

The various aspects of the present invention will be more fullyunderstood when the following portions of the specification are read inconjunction with the accompanying drawings wherein:

FIG. 1 is a front elevational view of the faces of the variousinstruments which comprise the device of the present invention;

FIG. 2 is a block diagram of the improved critical ectopic beat detectorof the present invention; and

FIG. 3 is a schematic view showing the various wave forms along a timebase.

It has been found that a person who has suffered cardiac difficulty,such as a heart attack, may experience ectopic heart beats, which arerandom occurring beats due to heart irritation. These will notnecessarily occur regularly in each normal heartbeat cycle, but willoccur intermittently. However, when they do occur, they usually willbear a timed relationship to the R-waves. It has been found that if suchectopic beats fall on the T-wave, which follows the R and S-waves, thereis the possibility that fibrillation may occur. Generally, however, theectopic beat normally occurs after the T-wave so that fibrillation isnot started by the simultaneous occurrence of the ectopic beat and theT-wave. If the ectopic beat starts approaching the T-wave, this isusually an indication that it will continue to approach it until suchtime as it is superimposed on the T-wave, and when this occursfibrillation may occur. However, if it is observed that the ectopic beatis approaching the T-wave, medication can usually be given to thepatient in advance of its reaching the T-wave and thus forestall thefibrillation which could otherwise occur. The ectopic beat detector ofthe present invention is capable of detecting whether the ectopic beatis approaching the T-wave to permit the timely giving of medication tothe patient.

The normal heartbeat is shown at 10 in FIGS. 2 and 3. This heartbeat,insofar as pertinent here, includes an R-wave and a T-wave, which issubsequently followed by another R-wave. The Q and S portions of theheartbeat are shown in FIG. 3 but will not be referred to hereafterinasmuch as they are not pertinent to the present subject matter. Adamaged heartbeat is shown at 11 in FIGS. 2 and 3, and includes aR-wave, a T-wave and an ectopic beat E which is followed by a subsequentR- wave. As noted above the heart may produce normal wave forms 10 for aperiod of time and occasionally include an ectopic beat E. In essence,heartbeat waveform 11 is normal waveform 10 plus an ectopic beat E.Normally this ectopic beat falls between the T-wave and the subsequentR-wave. As long as it stays a predetermined minimum distance from the T-wave, there usually is not any great danger of fibrillation. However, ifthe ectopic beat should move from the position E in FIG. 3 to theposition E, thereby showing a sliding to the left so as to approach theT-wave, there may be fibrillation in the future and this will usuallyoccur when the ectopic beat is superimposed on the T-wave.

The circuit of the present invention detects ectopic beats anddetennines whether they are sliding towards superimposition with theT-wave. The circuit includes a pair of electrocardiograph leads 12 and13 which may be coupled to any type of suitable sensing electrodes, suchleads also being coupled to potentiometer 14 which picks up the requiredvoltage. The heartbeat waveforms 10 or 11, as the case may be, arepassed from potentiometer 14 to high pass filter 15 which removes baseline wandering below one cycle. Thereafter the waveform is fed to the60-cycle rejection filter 16 which re jects any 60-cycle voltage whichappears on the signal, this voltage normally being picked up because ofthe patients proximity to 60-cycle wires. The signal is thereafter fedto the normal isolation transistor circuit which isolates the filter 16from low pass filter 18 to prevent interaction therebetween. The lowpass filter 18 cuts out high frequency, above cycles, due to artifactsfrom the patients muscle movement. The output from low pass filter 18 isfed to a conventional coupling circuit 19 which in turn transmits thesignal to the amplifier circuit 20 which is essentially an operationalamplifier which restores the signal level to overcome the previous loss.The output from amplifier circuit 20 is fed to both positive clippercircuit 21 and negative clipper circuit 22 which cut out the noise dueto muscle artifacts. This will cause the waveform to look like clippedform 23 of FIG. 2, if positive. The clipped waveform is thereafter fedto differentiator 24 which converts the clipped Signals to spikes andthis waveform is shown at 25 in FIGS. 2 and 3. It will be assumed thatwaveform 25 is one which has an ectopic beat therein. Therefore, spikes26 will be representative of the R-waves of the normal heartbeat andspike 27 will be produced by the ectopic beat E. It is the timedrelationship between the spike 26 formed by the R-waves and the spike 27formed by the ectopic beat which is used to determine whether theectopic beat is approaching the previous R- wave.

The output from differentiator 24 is fed to one-shot multivibrator 28which produces a 100 millisecond square wave output 29 or 30 every timethat it is triggered by a spike 26 or 27, respectively. The square waves29 and 30 in turn are used to trigger one-shot multivibrators 31 and 32.Multivibrator 31 is triggered at the tail end of waves 29 and 30 toprovide a 2- millisecond reset pulse 33 at the tail end of each R-wavegenerated square wave 29 and a 2-millisecond pulse 34 at the tail end ofthe ectopic beat generated square wave 30. The reset pulses 33 are fedto and trigger the free-running sawtooth generator 35 which will producea sawtooth wave output 36. As can be seen from FIG. 3 sawtooth wave 36will generally run from the end of one reset pulse 33 to the beginningof the next reset pulse 33 notwithstanding the possi ble existence of anectopic beat generated reset pulse 34 therebetween, which does notoccur, as explained in greater detail hereafter.

The output of the sawtooth generator 35 is coupled to a coupler poweramplifier 37 which in turn is coupled to a comparator circuit 38 throughlead 39. The comparator is a conventional circuit known as a 709Comparator and also has an input thereto from potentiometer 40 whichsets the basic voltage which is to be compared to the sawtooth generatedvoltage 36. Comparator 38 may be of the type shown on page 165 of the1967 Edition of the Fairchild Semi-Conductor Linear Integrated CircuitsApplications Handbook. At this point it is extremely important to notethat the magnitude of the voltage of sawtooth wave 36 at any giveninstant is directly proportional to the time from the point at whichreset occurred, that is, since sawtooth wave 36 is formed by a straightline with a predetermined slope, in going upwardly from the lowermostreset point 41, the wave 36 will at any instant be a measure of theelapsed time from that point 41. Potentiometer 40 provides waveform Pwhich is a constant DC output, which is a representation ofa length oftime, that is, it is directly proportional to time, when considered inreference to the amplitude of sawtooth wave 36. Whenever the sawtoothwaveform 36 at any instant in time, such as the instant in timecorresponding to waveform 42, is less than the value of waveform P,there will be a negative output from comparator 38 which will be fedback to multivibrator 31 through lead 43 and thus prevent reset of thesawtooth generator, by preventing any pulse between reset pulses 33 frombeing used as a trigger to reset the sawtooth generator. ln other words,as can be seen from FIG. 3, the sawtooth wave 36 will be generated byand between adjacent reset pulses 33, that is, whenever the potential ofsawtooth wave 36 reaches the value of voltage P the comparator willprovide a positive signal to cause the reset pulses 33 to reset thesawtooth generator. Otherwise, reset will not occur.

In accordance with the present invention, a circuit is provided fordetermining whether the ectopic beat as represented by spike 27 isapproaching the T-wave. Since the T-wave is relatively smallelectronically and is difficult to measure, and since the T-wave bears apredetermined timed relationship to the R-wave as represented by spike26, the distance or time between the ectopic beat and the T-wave can bemeasured by the distance of the ectopic beat from the preceding R-wave.To this end, as noted above, spikes 26 and 27 are used to generatesquare waves 29 and 30, respectively. The leading edges of square waves29 and 30 are used to generate 2 millisecond sample pulses 44 and 42,respectively. The distance between sample pulse 44 and the subsequentsample pulse 42 is the same as the time between spikes 26 and 27 whichis the same as the time between wave R and ectopic beat E. These samplepulses 44 and 42 are utilized to determine whether the ectopic heat isapproaching the previous R wave. More specifically, a potentiometer 47is provided which has its output coupled to comparator 45, which is alsocoupled to the output of coupler-amplifier 37 through lead 46'. Thuscomparator 45 which may be of the 709 type, as described above, comparesthe voltage of potentiometer 47 with the output of the sawtoothgenerator 35. The voltage level of potentiometer 47 is shown at M inFIG. 3. Potentiometer 47 is set at any determined level, as explained indetail hereafter, and the magnitude of the voltage is a measure of timebecause voltage P is a measure of time, and the magnitude of sawtoothwave 36 is a measure of time. The comparator 45 will provide a positiveoutput only if the value of the sawtooth wave 36 is less than the valueof the voltage M. Otherwise there is a negative output. The output ofsample multivibrator 32 is coupled to AND logic computer 46 by lead 48,along with the output of comparator 45. AND logic 46 may be of the typeshown in the paragraph entitled Gating Circuits on page 83 of the RCATransistor Manual, Technical Series SCl 3, Edition of 8-67, Copyrighted1967. If the magnitude of sawtooth wave 36 at the time of sampling isgreater than the potential of the M voltage, as would be the case attime 49, there would be a negative output from the comparator 45, If atthe time a sample pulse 42 or 44 is applied to the AND logic 46, thisnegative output is applied by comparator 45 to AND 46, there will be nooutput from the AND, because the NAND will only provide an output if thesample pulse and the comparator 45 output are both positive. Time 49 iswhen sample pulse 42 occurs a sufficiently long time after sample pulse44, that is, when the ectopic beat is sufficiently long after theprevious R-wave and therefore sufficiently far removed from the previousT-wave. However, if for any reason the ectopic beat E should startshifting to the left so that it would assume the location at E and thusgenerate a spike 27' which in turn would generate a square wave 30 andin turn produce a sample pulse 42' at time 50, at this point the Mvoltage would be greater than the voltage of the sawtooth generatedvoltage 36, and thus indicate that a shorter time has elapsed from theprevious R-wave than elapsed to the time 49. This being the case, theAND logic circuit would be energized because the output from thecomparator was positive at the same time that positive pulse 42occurred. The AND 46 will therefore energize the latching alarm circuit51 coupled thereto which in turn would ignite the alarm lamp 52 and alsoclose latching circuit 53 coupling the sawtooth generator 35 to digitalindicator 54 via leads 55 and 56. This will cause a voltage to beapplied to the digital indicator, and the magnitude of this voltage willbe caused to remain constant because of the connection between thelatching alarm circuit 51 and the sawtooth generator 35 through lead 57.As noted above, the magnitude of the sawtooth wave at any given instantis a measure of time from the last R-wave at which it was reset.Therefore when the voltage is stopped by the latching alarm circuit, itis this voltage of the sawtooth generator which is applied to thedigital indicator 54 to provide a read-out at 58 which shows the numberof milliseconds which transpired between the previous R-wave and thesubsequent ectopic beat E. It will be appreciated that when samplepulses 44 are applied to AND 46, the magnitude of the sawtooth voltage36 must be greater than voltage M to cause the comparator to provide anegative output and therefore AND 46 will not be actuated at this timebecause, as noted above, a positive pulse from comparator 45 must besensed by AND 46 at the same that a positive pulse is provided bymultivibrator 32. Thus, sample pulses 44, generated by the R- wavescannot actuate the alarm circuit because, at this time, comparator 45produces a negative output.

The faces of the various units containing the circuits of FIG. 2, areshown in FIG. 1. As can be seen, the digital indicator 54 is shown whichhas a digital read-out window 58. This digital read-out is obtained whenlatching switch 53 is closed and it will show the time which has elapsedbetween a previous R- wave and a subsequent ectopic beat as explained indetail above. If desired, a digital print-out device, which isconventional in the art, may be substituted for digital indicator 54 soas to provide a written record.

The device also includes a computer unit 63 which contains all of thecircuit components except the digital indicator 54 and the oscilloscope61 which receives its input from the electrocardiograph lead 62. Theface of the computer unit 63 includes the alarm lamp 52, noted above,which ignites when the ectopic beat occurs within a predetermined timeafter the previous R-wave. ln order'to set the minimum desired timebetween a previous R-wave and the ectopic interval, a knob 60 isprovided surrounding a movable counter 60. Knob 60 is manipulated toplace in the window the minimum desired time between an R-wave and asubsequent ectopic beat and this causes a corresponding voltage to beprovided by potentiometer 47 which in turn provides the voltage Mdescribed in detail above.

At this point itis to be noted that the computer also includes a resetbutton 64 which is utilized to reset the latching alarm circuit 51 afterit has been energized. A R-wave lamp 65 is also provided which igniteswith every R-wave. This lamp is shown in FIG. 2 and it is coupled tomultivibrator 28 and is ignited whenever this multivibrator isenergized. This provides a visual indication every time there is a heartbeat or ectopic beat. Thus by observing this light, if there is noectopic beat, there will be an equal time interval between adjacentR-waves. On the other hand, if there is an ectopic beat, there will bean occasional irregularity in the interval between the times that theR-wave light lights up and this will serve to provide an indication ofthe ectopic beat.

The computer unit also includes a sensitivity control 66 which isessentially the voltage take-off associated with potentiometer 14 (FIG.2). This provides the optimum selectivity between the electrocardiographsignal and the inherent muscle noise and thus discriminates againstelectrical noise. The computer also includes a knob 63 which isassociated with potentiometer 40 to set it at the normal R-waveinterval. This is accomplished by closing marker switch 67 which couplesone shot multivibrator 68 to cathode ray oscilloscope 61 on which theheartbeat waveform is displayed. It can readily be seen that when switch67 is closed, the one shot multivibrator will energize the deflectioncircuits of oscilloscope 6]. Multivibrator 68 in turn is energized everytime there is a positive output from comparator 45 and comparator 38. Asnoted above, comparator 45 will be energized to provide a positiveoutput as soon as the sawtooth voltage is less than the voltage producedby potentiometer 47. This occurs approximately at time 50. Thus, asquare wave will tend to be generated on the oscilloscope 61 at thistime. This square wave is of twenty millisecond duration, and itsmagnitude is approximately the magnitude of the R-wave. However, sincethe magnitude is reached almost instantaneously with the triggering ofthe multivibrator, the vertical traces of the square wave will notappear on the scope. However, since the square wave is of twentymilliseconds duration, there will be a horizontal sweep produced by themultivibrator for this period at the magnitude of the R-wave and thiswill appear as a very short line or dot 71 on the scope. Therefore,multivibrator 68 will provide a dot on the scope whenever comparator 45is energized at time 50. This dot will appear somewhere between adjacentR-waves. If the actual ectopic beat E is to the right of dot 70, it isin the safe zone; if it is to the left, it shows that it has approachedthe T-wave, away from the safe zone. However, in order to set theR-waves relative to each other so that the dot 70 will be synchronizedtime-wise relative to the R- waves, knob 63' is used which sets thevalue of potentiometer 40. This will cause a dot 70 to appear on thescope every time the sawtooth voltage triggers the comparator 38, andthis will occur only when the magnitude of the sawtooth is approximatelythe same magnitude as the voltage P to cause comparator 38 to provide apositive output. This can be seen from FIG. 3 from which it will be seenthat reset of the sawtooth wave 36 will occur when the sawtooth wave isof a magnitude of voltage P. Therefore, the higher the voltage P, thelonger will be the length of the sawtooth, and the lower the voltage P,the shorter the length of the sawtooth, and thus the voltage P is ameasure of the time between subsequent R-waves. The dots 70 and 71 givea visual indication on the scope of the relative positions betweenadjacent R-waves and the minimum desired time between an ectopic beatand the preceding R-wave. In actual use, when dots 70 and 71 are causedto appear on the scope, an attendant can observe whether the ectopicbeat, as seen on the heartbeat waveform on the scope, is approaching thedot 71 and this can provide the attendant with a visual indication ofsuch an approach before the alarm circuit described above is actuated.

Quantitatively, the general time between adjacent R-waves is between 800and 1,000 milliseconds for most patients. The T-wave will normally occurbetween 200 and 500 milliseconds after the preceding R-wave. Generallyif there is an ectopic beat, it will fall at approximately 650milliseconds after the preceding R-wave and these ectopic beats willremain at this time interval. However, ifit is seen on the oscilloscopethat the ectopic beats start approaching the R-waves so as to approachthe 200 to 500 millisecond range in which the T-wave falls, medicationcan be given to desensitize the patient. The dial 60' is usually set atabout 500 milliseconds to provide an alarm in the event the ectopic beatstarts approaching the T-wave.

We claim:

1. A critical ectopic beat detector for providing a warning that anectopic beat is approaching a critical portion of a heartbeat comprisingfirst circuit means for monitoring a heartbeat including means fordetecting a predetermined normal portion of a heartbeat and fordetecting an ectopic beat, second circuit means for measuring the timerelationship between said normal portion of said heartbeat and saidectopic beat, and third circuit means for providing an indication ofwhen said ectopic beat bears a predetermined timed relationship to saidnormal portion of said heartbeat, said third circuit means includingmeans for providing an alarm signal when said predetermined timedrelationship is experienced, said heartbeat including a R-wave andwherein said first circuit means comprises first means for providing afirst impulse each time that it is triggered by a R-wave and a secondimpulse when triggered by said ectopic beat, second means triggered bysaid first means to provide a reset pulse every time said first means istriggered by said R-wave, a free-running sawtooth generator coupled tosaid second means and triggered by said reset pulses to periodicallyreset said sawtooth generator whereby the magnitude of said sawtoothvoltage at any particular time is a measure of elapsed time from eachreset pulse and therefore from said R-wave, comparator means coupled tosaid sawtooth generator, potentiometer means coupled to said comparatorto provide a voltage which is a measure of minimum desired elapsed timebetween said R-wave and a subsequent ectopic beat, said comparatorcomparing said sawtooth voltage with the output of said potentiometermeans at the time of said ectopic beat to provide a first type of outputwhen said potentiometer voltage is in excess of said sawtooth voltageand a second type of output when said potentiometer voltage is less thansaid sawtooth voltage, fourth circuit means coupling said comparator tosaid third circuit means for providing said third signal whenever saidfirst type of output is obtained signifying that the elapsed timebetween said R-wave and said subsequent ectopic beat is less than saidpredetermined minimum, said first means comprising a first multivibratorfor providing a first square wave of relatively long duration and saidsecond means comprising a second multivibrator providing a second squarewave of relatively short duration at a first predetermined portion ofeach of said first square waves, means for preventing said second squarewaves produced at the time of said ectopic beat from resetting saidsawtooth generator, third means comprising a third multivibrator forproviding a third square wave of relatively short duration at a secondpredetermined portion of said first square wave for acting as a samplepulse, a second comparator coupled to said sawtooth generator, secondpotentiometer means coupled to said second comparator for providing avoltage which is proportional to the time between adjacent R-waves,

and said third circuit means including a logic circuit coupled to saidthird multivibrator and periodically energized by said sample pulses.

1. A critical ectopic beat detector for providing a warning that anectopic beat is approaching a critical portion of a heartbeat comprisingfirst circuit means for monitoring a heartbeat including means fordetecting a predetermined normal portion of a heartbeat and fordetecting an ectopic beat, second circuit means for measuring the timerelationship between said normal portion of said heartbeat and saidectopic beat, and third circuit means for providing an indication ofwhen said ectopic beat bears a predetermined timed relationship to saidnormal portion of said heartbeat, said third circuit means includingmeans for providing an alarm signal when said predetermined timedrelationship is experienced, said heartbeat including a R-wave andwherein said first circuit means comprises first means for providing afirst impulse each time that it is triggered by a R-wave and a secondimpulse when triggered by said ectopic beat, second means triggered bysaid first means to provide a reset pulse every time said first means istriggered by said R-wave, a free-running sawtooth generator coupled tosaid second means and triggered by said reset pulses to periodicallyreset said sawtooth generator whereby the magnitude of said sawtoothvoltage at any particular time is a measure of elapsed time from eachreset pulse and therefore from said R-wave, comparator means coupled tosaid sawtooth generator, potentiometer means coupled to said comparatorto provide a voltage which is a measure of minimum desired elapsed timebetween said R-wave and a subsequent ectopic beat, said comparatorcomparing said sawtooth voltage with the output of said potentiometermeans at the time of said ectopic beat to provide a first type of outputwhen said potentiometer voltage is in excess of said sawtooth voltageand a second type of output when said potentiometer voltage is less thansaid sawtooth voltage, fourth circuit means coupling said comparator tosaid third circuit means for providing said third signal whenever saidfirst type of output is obtained signifying that the elapsed timebetween said R-wave and said subsequent ectopic beat is less than saidpredetermined minimum, said first means comprising a first multivibratorfor providing a first square wave of relatively long duration and saidsecond means comprising a second multivibrator providing a second squarewave of relatively short duration at a first predetermined portion ofeach of said first square waves, means for preventing said second squarewaves produced at the time of said ectopic beat from resetting saidsawtooth generator, third means comprising a third multivibrator forproviding a third square wave of relatively short duration at a secondpredetermined portion of said first square wave for acting as a samplepulse, a second comparator coupled to said sawtooth generator, secondpotentiometer means coupled to said second comparator for providing avoltage which is proportional to the time between adjacent R-waves, andsaid third circUit means including a logic circuit coupled to said thirdmultivibrator and periodically energized by said sample pulses.